1. Field of the Invention
The present invention relates to a method and apparatus for precisely measuring the surface shape of a golf ball, e.g., the shapes of dimples.
2. Related Art
In order to improve the travel performance of a golf ball, a large number of dimples--which may be of a single kind of shape or of plural kinds of shapes--are provided on the surface of the golf ball. In general, such dimples are formed during a molding process in which a molding material is injected into the cavity of a mold that has on its cavity wall surface protrusions corresponding to the dimples, and the injected molding material is then hardened.
Although to the casual observer the dimples of a golf ball appear uniform, the shapes of the dimples are affected by the machining accuracy of a mold, wear of the cavity wall surface of the mold due to prolonged use, distortion of molding material due to hardening, and polishing and painting after molding of the ball. Therefore, measurement must be performed so as to check whether the dimples have been formed into a target or desired shape.
Conventionally, the shapes of dimples have been measured as follows. Light from a lamp such as an incandescent lamp is passed through a slit to obtain a light beam having the cross section of a line (hereinafter called "a line-shaped light"), which is then radiated onto a dimple of a golf ball placed on a base. The image of the irradiated portion is captured through use a camera, and the depth of the dimple is measured from the thus-obtained image. More specifically, when the above-described line-shaped light is radiated onto a dimple at, for example, the central portion thereof (i.e., along the diametrical line), the irradiated portion is displayed on, for example, a monitor screen as having a concave cross-sectional shape. The displayed cross section is then divided at predetermined intervals from one edge to the other edge, and the depth of the dimple is measured at each of the divided portions.
However, when light emitted from a lamp and passed through a slit is radiated as a line-shaped light onto a dimple of a golf ball, the light scatters on the dimple. Therefore, the method of measuring the shapes of dimples based on an image obtained through use of line-shaped light unavoidably decreases the measurement accuracy, and therefore is not suitable for measurement of the shapes of dimples of a golf ball.